1. Field of the Invention
The present invention relates to an internal power supply voltage control apparatus for generating a low voltage and applying it to an internal circuit, and more particularly, to an internal power supply voltage control apparatus capable of carrying out a low voltage margin test and a high voltage margin test such as a burn-in test or a stress test.
2. Description of the Related Art
High speed semiconductor memory devices have recently been used in personal computers and workstations.
In response to demands for a lower power supply voltage and a lower power consumption, a high speed semiconductor memory device is divided into a peripheral circuit operated directly by an external power supply voltage and an internal circuit having low breakdown voltage characteristics operated by a voltage lower than the external voltage.
In order to perform a voltage margin test upon the above-mentioned internal circuit, various internal power supply voltage generating apparatuses have been suggested.
In a first prior art internal power supply voltage control apparatus (see: JP-A-2000-156097), a reference voltage generating circuit receives a control signal supplied from an externally-provided pad to generate a reference voltage which is supplied to an internal power supply reference voltage generating circuit for generating an internal power supply reference voltage in accordance with the reference voltage. The internal power supply reference voltage is further supplied to an internal power supply voltage generating circuit for generating an internal power supply voltage in accordance with the internal power supply reference voltage. This will be explained later in detail.
In the above-described first internal power supply voltage control apparatus, however, since the externally-provided pad for the control signal is necessary, the apparatus would be increased in size. Also, it is impossible to accurately confirm the actual internal power supply voltage for the low voltage margin test mode. Further, since the internal power supply voltage for the low voltage margin test mode is fixed, it is impossible to determine a lower limit of the low voltage margin test mode. Additionally, since the internal power supply voltage cannot be higher than the external voltage, a high voltage margin test such as a burn-in test or a stress test cannot be performed upon the internal circuit.
In a second prior art internal power supply voltage control apparatus (see: JP-A-5-33116), an internal power supply voltage generating circuit for generating an internal power supply voltage for a normal operation mode and an externally-provided pad to which an internal power supply voltage for a voltage margin test mode is applied are switched by a selecting circuit. Thus, since the internal power supply voltage for a voltage margin test mode can be changed, not only a lower limit of the low voltage margin test mode but also a higher limit of the high voltage margin test mode can be determined. This also will be explained later in detail.
In the above-described second prior art internal power supply voltage control apparatus, however, since the two externally-provided pads are necessary, the apparatus would be increased in size.
In the above-described second prior art internal power supply voltage control apparatus, the control signal can be supplied from an address input pad (see: JP-A-3-160699); in this case, the number of externally-provided pads can be decreased. However, the externally-provided pad for the control signal is still necessary.
In a third prior art internal power supply voltage control apparatus, the first prior art internal power supply voltage control apparatus is combined with the second prior art internal power supply control apparatus. This also will be explained later in detail.
Even in the above-described third prior art internal power supply voltage control apparatus, however, since the two externally-provided pads for the control signal and the internal power voltage are necessary, the apparatus would be increased in size.
In a fourth prior art internal power supply voltage control apparatus, the selecting circuit of the third prior art internal power supply voltage control apparatus is replaced by a test mode entry circuit and a test mode selecting circuit. Also, in a voltage margin test mode, the internal power supply reference voltage generating circuit and the internal power supply voltage generating circuit of the third prior art power supply voltage control apparatus are deactivated by a canceling signal of the test mode selecting circuit. In this state, a driver in the internal power supply voltage generating circuit is completely turned ON. Therefore, if a low voltage or a high voltage as a voltage margin test mode is applied to an external pad for the external voltage, such a low voltage or such a high voltage is supplied via the driver to the internal circuit. Thus, an arbitrary voltage margin test can be carried out, without the externally-provided pad for the internal voltage while the externally-provided pad for the control signal is necessary. This also will be explained later in detail.
Thus, in the above-described fourth prior art internal power supply voltage control apparatus, in a voltage margin test mode, since the external voltage can be low or high, not only a low voltage margin test but also a high voltage margin test such as a burn-in test or a stress test can be carried out.
In the above-described fourth prior art internal power supply voltage control apparatus, however, in a voltage margin test mode, a circuit portion such as a peripheral circuit operated directly by the external voltage is also subjected to a low voltage or a high voltage for the voltage margin test mode, so that it is impossible to accurately determine a lower limit of the low voltage margin test mode and an upper limit of the high voltage margin test mode.
In the above-described fourth prior art internal power supply voltage control apparatus, the internal power supply reference voltage of the internal power supply reference voltage generating circuit can be adjusted to be a low voltage or a high voltage. Even in this case, it is impossible to accurately determine a lower limit of the low voltage margin test mode and an upper limit of the high voltage margin test mode.
In a fifth internal power supply voltage apparatus, an internal power supply voltage for a voltage margin test mode is also applied from an externally-provided pad to the internal power supply voltage generating circuit of the fourth internal power supply voltage apparatus. As a result, in a voltage margin test node, the internal power supply reference voltage generating circuit is deactivated, while a low voltage or a high voltage is supplied as the internal power supply voltage to the internal power supply voltage generating circuit. Therefore, the internal power supply voltage is brought close to the above-mentioned low voltage or high voltage as a voltage margin test mode, and thus, an arbitrary voltage margin test can be carried out. This also will be explained later in detail.
In the above-described fifth prior art apparatus, however, after a semiconductor device (chip) is completed, no use is made of the internal power supply voltage due to no wire bonding operation upon the pad thereof, so that a high voltage margin test such as a burn-in test or a stress cannot be carried out.
In a sixth prior art internal power supply voltage control apparatus, a burn-in test mode circuit is incorporated into to the elements of the above-described fifth prior art internal power supply voltage control apparatus. This also will be explained later in detail.
In the above-described sixth prior art internal power supply voltage control apparatus, however, when the breakdown voltage of transistors due to the fluctuation of manufacturing process or the like, the voltage margin in a burn-in test mode and the guaranteed range of operation is decreased, so that it is impossible to surely carry out a burn-in test.
It is an object of the present invention to provide an internal power supply voltage control apparatus capable of accurately carrying out a voltage margin test without additional externally-provided pads.
According to the present invention, in an internal power supply voltage control apparatus, a reference voltage generating circuit generates a reference voltage. A first internal power supply reference voltage generating circuit generates a first internal power supply reference voltage in accordance with the reference voltage, and a second internal power supply reference voltage generating circuit generates a second internal power supply reference voltage in accordance with a voltage applied to a predetermined pad. A test mode selecting circuit activates one of the first and second internal power supply reference voltage generating circuits in accordance with a control signal. An internal power supply voltage generating circuit generates an internal power supply voltage in accordance with one of the first and second internal power supply reference voltages generated from an activated one of the first and second internal power supply reference voltage generating circuits.
The voltage at the predetermined pad serves as a low voltage or a high voltage for a voltage margin test mode.